The present invention relates to the purification of depleted bright nickel electroplating baths.
Brighteners and leveling agents are commonly added to nickel plating baths to produce improved brightness and leveling of the plating layer in the final nickel plated article. Pyridine compositions such as 1-(3-sulfopropyl)-pyridinium betaine (PPS) or 1-(3-sulfo-2-hydroxypropyl)-pyridinium betaine are commonly used as additives for this purpose.
During the typical extended use of commercial plating baths containing pyridine brightening and leveling agents, the performance of the bath decreases until the bath has degraded to such an extent that it is necessary to rejuvenate or replace the bath. As a result of this degradation, the brightening and leveling characteristics of the bath are dramatically reduced or may be reduced to such an extent that the bath is no longer viable for electroplating.
There have been several types of methods attempted in the past to remedy this depleted condition. For example, in the early stages of degradation the mere addition of more pyridine agents will temporarily improve the bath. However, the bath will eventually further degrade to such an extent that further additions will no longer improve the condition of the bath. Other methods include treating the bath with activated charcoal and filtration of the bath. While these methods are again adequate at the initial degradation states, the bath eventually becomes untreatable in this manner and may have to be entirely replaced. A more complex method of rejuvenation is shown in U.S. Pat. No. 3,122,490 which includes the addition of sultones and lactones while heating the bath to relatively high temperatures for regeneration of the bath. While this process may have somewhat improved results over the activated carbon and filtration processes, the process is not universally commercially practical since most tank linings cannot tolerate the temperature requirements.
Therefore, there has been a need in the art to provide a method for purification of such a degraded nickel bath which will allow increased life of the nickel bath without adversely effecting the basic function thereof.